feat(isac): support deferred item icons

docs/DESIGN_SYSTEM.md

@@ -1222,3 +1222,19 @@ Use explicit textual tier capacity wherever Gear tier is summarized: `1 MOD
 SLOT` for T0 and `2 MOD SLOTS` for T1/T2. On narrow screens the identity band
 and preview controls stack, while repeated quality data may scroll rather than
 compressing numeric controls below usable sizes.
+
+### Deferred game-data icons
+
+Game-data icons are optional enrichment, never a blocker for creating or
+proposing a canonical item. Upload fields must state that an icon may be
+contributed later and show the shared `/missing-item-icon.svg` artwork when no
+upload exists. Registries, relationship rails, and builder selection controls
+use the same placeholder instead of initials, empty boxes, or ad hoc glyphs.
+
+Treat the placeholder as an explicit incomplete-data state: keep its subdued
+SHD styling and useful alternative text where the surrounding item name is not
+already available. Do not persist placeholder metadata or copy the placeholder
+into per-item storage. A later contributor replaces it through the normal icon
+upload proposal, preserving the canonical record and audit history. The upload
+itself retains all transparent-format, size, SVG-safety, focus, drag/drop, and
+paste validation requirements.